class Solution7 {

    boolean[][] vis;
    int m, n;
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};

    public int numIslands(char[][] grid) {
        m = grid.length; n = grid[0].length;
        vis = new boolean[m][n];

        int ret = 0;
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(grid[i][j] == '1' && !vis[i][j]){
                    dfs(grid, i, j);
                    ret++;
                }
            }
        }
        return ret;
    }

    public void dfs(char[][] grid, int i, int j){
        vis[i][j] = true;

        for(int k = 0; k < 4; k++){
            int x = i + dx[k], y = j + dy[k];
            if(x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && !vis[x][y]){
                dfs(grid, x, y);
            }
        }
    }
}